KR870004072Y1 - Perceptive circuit for absolute humidity of microwave oven - Google Patents

Abstract

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Description

Absolute Humidity Detection Circuit of Microwave Oven

1 is a circuit diagram of the present invention.

2 is an output voltage waveform diagram of a sensor unit.

3 is an output voltage waveform diagram according to the absolute humidity of the cooking chamber of the absolute humidity sensor in the sensor unit.

4 is a current-voltage curve diagram of an absolute humidity sensor according to a sensor supply voltage under each sensor ambient temperature.

* Explanation of symbols for main parts of the drawings

2: voltage conversion part 3: sensor part

ZD ₁ , ZD ₂ : Zener Diode RL ₁ : Relay

OP ₁ -OP ₂ : Comparator OP ₃ : Operational Amplifier

Q ₁ , Q ₂ : Transistor TH ₁ , TH ₂ : Absolute Humidity Sensor

R ₁ -R ₁₃ : Resistor C ₁ , C ₃ : Capacitor

The present invention relates to an absolute humidity detection circuit of a microwave oven so that the absolute humidity sensor installed inside the cooking chamber for the automatic cooking function of the microwave oven can perform an optimal function.

In a conventional microwave oven, a gas sensor, an infrared sensor, or a relative humidity sensor is installed in a cooking chamber to detect a state where food is cooked by these sensors, and automatic cooking is realized by inputting the detected signal into a microcomputer. The amount of food to be cooked during use is limited, and the location of food to be placed in the cooking chamber must be set to be constant, and the above sensor cannot be operated when cooking at 100 ° C. or higher. Although microwave ovens have been used, the above-mentioned absolute humidity sensor has to be heated to a self-heating state of 200 ° C to 250 ° C in order to detect the absolute humidity in the cooking chamber that changes according to the progress of food. As shown in the figure, as the ambient temperature decreases, the voltage supplied to the absolute humidity sensor Only when it is set high, it can be seen that the absolute humidity sensor made of thermistor enters the self-heating state. In the above absolute humidity sensor was not working properly closed.

The present invention is to improve the disadvantages of the prior art as described above, by increasing the supply voltage to the absolute humidity sensor from the initial state of automatic cooking to the self-heating state to promote the intrusion into the self-heating state When the absolute humidity sensor enters the self-heating state, the normal supply voltage is maintained again so that the automatic cooking function of the microwave oven is maintained in the optimum state.

The voltage converting unit 2 for converting the supply power to the absolute humidity sensor composed of the respective thermistors TH ₁ and TH _{2 in the} normal sensor unit 3 includes a constant voltage transistor Q ₁ and its base voltage. Setting Zener Diodes ZD ₁ (ZD ₂ ), Relays RL ₁ , Relay Driving Transistors Q ₂ , and Comparators OP That the Output Terminals Are Common to the Microcomputer 5 Via the Normal Interface Circuit 6 (OP) ₁ ) and comparator (OP ₂ ), delay capacitor (C ₁ ) (C ₂ ) and resistor (R ₁ -R ₈ ), where Vcc is DC power, AC is AC power, 1 Silver DC power supply circuit, 4 analog / digital converters, 5 microcomputers, 6 interface circuits, 7 key control panel (7) with built-in auto-selection key and start switch, 8 magnetron drive unit, R ₉ -R ₁₃ represents a resistor, OP ₃ represents an operational amplifier, MGT represents a magnetron, RL ₂ represents a relay, Q ₃ represents a transistor, and A and B represent each point.

The operation and effects of the present invention as the configuration is as follows.

An absolute humidity sensor in the sensor unit 3 consists of a surface-type deoeo Mr (TH ₁₎ and a closed deoeo Mr (TH ₂₎ in a sealed state to the dry air having the same operating characteristics, in the cooking chamber in the course of the food is cooked When containing the water vapor generated air is brought into contact with the exposure-type deoeo Mr (TH ₁₎ increasing the self-electric resistance of the deoeo Mr (TH ₁₎ by vaporization phenomenon while closed deoeo Mr (TH ₂₎ is outside air and the sealed In this state, the resistance value is kept constant, whereby a potential difference occurs between the A and B points, and the voltage caused by the potential difference is amplified by the operational amplifier OP ₃ .

The output of the operational amplifier OP ₃ rises as the cooking time elapses as shown in FIG. 2, which is again converted into a digital signal through the analog / digital converter 4 and the interface circuit 6. The microcomputer 5 is forced through the microcomputer 5, whereby the microcomputer 5 automatically controls the magnetron drive unit 8 by the built-in program.

On the other hand, as described above, the absolute humidity sensor composed of the respective thermistors TH ₁ (TH ₂ ) in the sensor unit 3 is supplied with Vcc power through the current limiting resistor R ₉ to generate 200 by self-heating. It is heated to -250 ℃, that is, it enters the self-heating state which can sense the absolute humidity in the cooking chamber, for example, current limit so that the absolute humidity sensor can enter the self-heating state at the sensor ambient temperature of 25 ° C. If the resistance (R ₉ ) is set, in the conventional case, since the supply voltage to the absolute humidity sensor should be relatively high as shown in FIG. 4 at the sensor ambient temperature of 25 ° C. or lower, the absolute humidity It often happens that the sensor does not enter the self-heating state and loses absolute humidity sensing capability.

The circuit operation state in the case where the voltage converter 2 of the present invention is installed on the Vcc power line that is the supply voltage to the absolute humidity sensor will be described in detail.

In the automatic cooking mode, the initial power is turned on and the start signal is inputted by the key control unit 7 to the microcomputer 5 through the interface circuit 6. In this case, the microcomputer 5 converts the voltage converter 2 into the microcomputer 5. When the output of the comparator OP ₁ in the output is 'LOW', the transistor Q ₃ in the magnetron driver 8 is turned “on” through the interface circuit 6 to thereby turn on the relay RL ₂ . Excitation causes the magnetron (MGT) to oscillate.

That is, when the initial power is turned on, the (+) input terminal of the comparator (OP ₁ ) is applied the Vcc voltage divided by the resistor (R ₃ ) (R ₄ ), and the (-) input terminal is the 'HIGH' output of the comparator (OP ₂ ). the output of the resistor (R ₅₎ and a condenser until a 'HIGH' level after the delay circuit (C ₁₎ is so maintained at a 'LOW' level comparator (OP ₁₎ is a 'HIGH', the transistor of relayed by the conduction of the (Q ₂₎ (RL ₁₎ is driven in its relay contacts there is piped into the zener diode (ZD _1), that when the Zener diode (ZD ₁₎ the zener voltage (V _ZD1) of normal voltage supply embrace of the Zener diode (ZD _2), the Zener voltage (V _ZD2) absolute Vcc voltage supplied to the humidity sensor is a Zener diode (ZD ₂₎ in more driving sensor part 3 by the main surface to hold a high voltage transistor (Q ₁₎ for the the normal, which is determined by the voltage higher than Vcc deoeo Mr (TH ₁₎ (TH ₂₎ absolute humidity sensor is easily self-heating phase consisting of It is a rush.

In this state, after the delay time T ₁ of the resistor R ₆ and the capacitor C ₂ in the voltage converter ₂ , the positive input terminal of the comparator OP ₂ is set to the 'HIGH' level. The output of the comparator OP ₂ is 'HIGH', and this 'HIGH' level output is (-) of the comparator OP ₂ after the delay time T ₂ by the resistor R ₅ and the capacitor C ₁ . As the input stage becomes the 'HIGH' level, the output stage of the comparator OP ₁ is inverted to the 'LOW' level after the delay time (T ₁ + T ₂ ) in the 'HIGH' level state after the power is turned on. When the output of the comparator OP ₁ is inverted to the 'LOW' level, the transistor Q ₂ is "cut off", whereby the relay RL ₁ is also "off", so that the relay contact is Zener diode ZD ₂ . as the connection, so absolute voltage Vcc supplied to the humidity sensor of the sensor part 3 by the driving of the constant-voltage transistor (Q ₁₎ for the voltage to fall as usual, and at the same time The comparator as sulhan the microcomputer 5 by the 'LOW' output of the (OP ₁₎ through the interface circuit 6 controls the magnetron driving unit (8), thereby oscillating the magnetron (MGT).

That is, the magnetron in the magnetron driver 8 during the delay time T ₁ + T ₂ by each of the capacitors C ₁ (C ₂ ) and the resistors R ₅ and R ₆ in the above-described voltage change unit 2. When the oscillation of (MGT) is stopped, the absolute humidity sensor in the sensor unit 3 is supplied with a voltage higher than usual to generate a self-heating state. After the self-heating of the absolute humidity sensor is completed, that is, the delay time described above. After (T ₁ + T ₂ ), while the supply voltage to the absolute humidity sensor is normally maintained, the microcomputer 5 supplies the control signal to the magnetron driver 8 to control the oscillation of the magnetron MG T. This delay time (T ₁ + T ₂ ) is the capacitance and resistance (R ₅ ) of each capacitor (C ₁ ) (C ₂ ) in the voltage conversion unit 2 in consideration of the time when the absolute humidity sensor is in the self-heating state. Set the value of (R ₆ ) appropriately.

On the other hand, if the supply voltage to the absolute humidity sensor in the sensor unit 3 is always set high, it will easily deteriorate due to the large current flowing through the absolute humidity sensor. Therefore, the circuit of the present invention is a microwave oven circuit using an absolute humidity sensor. It becomes essential.

As described above, the present invention increases the supply voltage to the absolute humidity sensor only until the absolute humidity sensor enters the self-heating state, and after supplying the normal voltage again to the self-heating state, the microwave oven using the absolute humidity sensor. It is a useful design that can contribute to improving the reliability and quality of the product by maintaining the automatic cooking function of the optimum state.

Claims (1)

The voltage converting section 2 for converting the supply power to the absolute humidity sensor composed of the respective thermistors TH ₁ and TH _{2 in the} normal sensor section 3 includes a constant voltage transistor Q ₁ and its base voltage. Setting Zener diode ZD ₁ (ZD ₂ ), relay RL ₁ , relay driving transistor Q ₂ , and comparator OP whose output terminal is normally co-operated with the microcomputer 5 via the interface circuit 6. ₁ ) an absolute humidity sensing circuit of a microwave oven, comprising a comparator (OP ₂ ), a delay capacitor (C ₁ ) (C ₂ ), and a resistor (R ₁ -R ₈ ).